1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
2. Description of the Related Art
DRAM (Dynamic Random Access Memories) has been used as semiconductor storage devices. The DRAM includes a plurality of memory cells each of which is formed of a transistor and a capacitor. The capacitor includes a capacitive insulating film between a lower electrode and an upper electrode. Charge is held in the capacitive insulating film to store information.
FIG. 7 and FIG. 8 in JP2011-204751A disclose forming an aluminum oxide film and a zirconium oxide film by an ALD method respectively. The ALD method forms one molecular layer of an aluminum oxide film or a zirconium oxide film by carrying out a cycle including supplying material gas, purging the material gas, supplying O3 gas, and purging the O3 gas. Then, the cycle is repeated a plurality of times to form an aluminum oxide film and a zirconium oxide film with respective desired film thicknesses.
JP2000-31404A discloses that a metal oxide film such as an IrO2 film, an ITO film, an RHO2 film, an RuO2 film, or an MoO3 film is used as a part of the lower electrode (Paragraph [0013]).
In the DRAM, the connection between the lower electrode of the capacitor and a capacitive contact plug positioned under the lower electrode is established via a pad in order to ensure a pitch aligning margin (hereinafter occasionally referred to as a “contact pad”). The pad needs to have reduced resistance, and thus a metal layer, particularly tungsten, is used as a common pad material. Furthermore, as a method for forming the lower electrode, there is used the ALD method, which is excellent in step coverage and which can deal with miniaturization. When a metal oxide film is formed as the lower electrode by the ALD method, as described in JP2000-31404A, O3 gas, which has high oxidizability, is used to oxidize a metal material. However, the O3 gas oxidizes the pad formed of tungsten or the like to increase the electric resistivity thereof, thereby inhibiting the electric continuity between the lower electrode and the pad.